1. Field
The presently disclosed subject matter relates to a vehicle lamp including a projector headlight using an LED light source for a low beam, and more particularly to a vehicle lamp including a projector headlight having a favorable light distribution pattern that can conform to a light distribution standard for a headlight.
2. Description of the Related Art
A projector headlight for a low beam and/or a high beam is frequently incorporated into vehicle lamps, such as a headlamp, a position lamp, a turn-signal lamp, brake lamp, traffic lamp, etc. The projector headlight may allow a light-emitting area thereof to be reduced and therefore allows the vehicle lamp including the projector headlight to be minimized in comparison with other type headlights.
FIG. 7(A) is a schematic side cross-section view depicting basic structure in a conventional projector headlight, and FIG. 7(B) is a schematic diagram showing a fundamental light distribution pattern for driving on the left side of a roadway as formed by the headlight of FIG. 7(A).
According to the basic structure of the conventional projection headlight shown in FIG. 7(A), the projector headlight 80 includes: a light source 82; an elliptical reflector 83 in which a first focus thereof is located near the light source 82; a projector lens 85 which has a focus thereof located near a second focus of the elliptical reflector 83; and a shade 84 having a top edge located near the focus of the projector lens 85. Thus, an optical axis Z80 intersects substantially with an optical axis of the light source 82, both the first and second focuses of the elliptical reflector 83, the top edge of the shade 84 and the focus of the projector lens 85, respectively.
In the conventional projector headlight 80, a part of the light emitted from the light source 82 directly passes through the projector lens 85 and another part of the light indirectly passes through the projector lens 85 by reflecting on the elliptical reflector 83. In this case, because the shade 84 can shield an upward portion of the emitted light, the projector headlight 80 can form light distribution pattern P50 for a low beam as shown in FIG. 7(B). Marks VL, HL and CL80 are a vertical line, a horizontal line and a cut-off line formed by the shade 84, respectively.
In the above-described structure, the projector lens 85 is composed of a convex lens including an aspheric surface. Therefore, the light L50 that is refracted at an edge portion of the projector lens 85 may cause larger chromatic aberration than at a middle position of the projector lens 85. The chromatic aberration tends to occur near the cut-off line CL80 shown in FIG. 7(B) because the light that passes near the top edge of the shade after being reflected from the elliptical reflector 83 may be more easily gathered at the edge portion of the projector lens 85.
Thus, the above-described structure may include a problem in that the chromatic aberration causes an unclear cut-off line CL80 in the light distribution pattern P50 shown in FIG. 7(B). To help solve this problem, a projector lens has been disclosed in patent document No. 1 (Japanese Patent Application Laid Open S60-62001 which is in the same patent family as U.S. Pat. No. 4,562,519). The projector lens provides an upper and lower portion thereof with a refracting member. Therefore, the negative effect caused by the chromatic aberration may be reduced.
A shade is disclosed in patent document No. 2 (Japanese Patent Application Laid Open JP2005-044574 which is in the same patent family as U.S. Pat. No. 7,244,056). The shade is formed with relatively large thickness and extends downward in a direction towards the projector lens. Thus, the negative effect of the chromatic aberration may decrease because mixture light located at the edge portion of the projector lens can be increased.
However, LED light sources have been used as a light source for a vehicle lamp for several reasons, including because an LED chip has recently been able to provide high-power with low power consumption. In addition, LED light sources can emit various color lights including a white light that can be used for a vehicle headlight. Therefore, the LED light sources have been also used as a light source for a vehicle headlight.
When an LED light source for emitting white light is designed, the white LED light source may generally be composed of a blue LED chip and a yellow phosphor (or other wavelength conversion material). In this case, because the LED light source may include more light emission points (i.e., blue light LEDs with wavelength conversion layer(s)) as compared with a normal incandescent or other single light source bulb, the LED light source may cause a problem such as projecting blue light near the cut-off line CL80 while widely refracting light at the edge portion of the projector lens.
Therefore, a projector lens for the LED light source is disclosed in patent document No. 3 (Japanese Patent Application Laid Open JP2008-226542). The projector lens is made by integrally casting both a high refracting and dispersing resin and a low refracting and dispersing resin. Thus, the negative effect of the chromatic aberration may be decreased via the projector lens that is composed of two layer lens.
In a vehicle headlight using the LED light source, it is important for the headlight to effectively emit the light emitted from the LED light source via the projector lens with respect to light use efficiency. Consequently, the projector lens disclosed in patent document No. 1 and the shade disclosed in patent document No. 2 may not adequately solve the above-described problems in the vehicle headlight using the LED light source. The above-described conventional structure may shield many of the light emitted from the light source 82 with the shade 84 and cannot emit them forwards via the projector lens 85.
The projector lens disclosed in patent document No. 3 may be difficult to integrally cast while maintaining the accuracy thereof so as to conform a light distribution standard for a headlight. In addition, the projector lens may cause problems such that a shape thereof becomes thick, and therefore the projector may cause the projector headlight to become high cost and a decrease of the brightness.
The above-referenced Patent Documents are listed below and are hereby incorporated with their English abstracts in their entireties.                1. Patent document No. 1: Japanese Patent Application Laid Open S60-62001 and U.S. Pat. No. 4,562,519.        2. Patent document No. 2: Japanese Patent Application Laid Open JP2005-044574 and U.S. Pat. No. 7,244,056        3. Patent document No. 3: Japanese Patent Application Laid Open JP2008-226542        
The disclosed subject matter has been devised to consider the above and other problems, characteristics and features. Thus, an embodiment of the disclosed subject matter can include a vehicle lamp including a projector headlight using an LED light source for a low beam that can conform to a light distribution standard for headlights with respect to white chromaticity. In this case, if the LED light source for the projector headlight is composed of a blue LED and a yellow phosphor, the projector headlight can conform to a light distribution standard while reducing a negative effect of the chromatic aberration. The light source can also be configured with the relatively simple structure.